Magnesium product



Aug. 3 ,1926. 1594,34@

` H. E. BAKKEN MAGNESIUM PRODUCT Original Filed NOV- l. 1922 2Shasta-Shaw?. i

Patented Aug. 3, 1926.

UNITED STATES PATENT OFFICE.

HERMAN E. BAKKEN', 0F NIAGARA FALLS, NEW YORK, ASSIGNOR TO AMERICAN MAG-NESIUM CORPORATION, OF NIAGARA FALLS, NEW YORK, A CORPORATION OF NEWYORK.

MAGNESIUM PRODUCT.

Original application led November 1, 1922. Serial No. 598.292. Dividedand this application led December s, 1924.

My invention relates to the production of metallic magnesium in asubstantially chemically pure state and in such a unique form that itsuse in subsequent processes of manufacture is greatly facilitated. Inthe processes that are at present practiced, mag ncsium` when roducedfrom ores containing other meta s and-metalloids, is likely to becontaminated with them. For use in the mechanical arts, these impuritiesshould be removed, as it is found that they exert a marked influence onthe physical and chemical properties of the metal even when present inonly a limited degree. Some prior processes for producing pure magnesiuminvolve the production and condensation of magnesium vapor. The vapor iscondensed either in liquid or powder form depending on the conditions ofcondensation. If condensed in liquid form, impurities such as sodium,which may travel into the condenser from the metal being vaporized, arelikely to be present in the molten liquid. If condensed in the form ofpowder, further manipulation of the product involves difhculf ties.Powder is very diiicult to meltwithout excessive losses and is veryeasily oxidized, due to the large amount of' surface exposed. My processis particularly adaptedl for use in refining crude metal. It islapplicable also to obtaining pure metal from magnesium scrap, such ascastings, alloys, etc.

This application is a division of my application Serial No. 598,292,tiled November 1,' 1922, wherein I have,Y described and claimed my saidprocess.

My invention comprises the purification of magnesium by converting thesolid metal directly into the state of vapor and then 'condensing itdirectly into the crystallized 'state without intermediate liquefaction,and 1n particular it consists in the discovery of Asuitable means andconditions whereby such puriiication can be made practically operableand capable of being commercially;

carried out so as to produce pure magnesium at a reasonable cost, and inthe discovery andproduction as a new commercialv product, of a new lformof magnesium of high purity, easily'capable of further manipulation.

It is known that magnesium boils at atmospheric pressure at about -1120C. -Puri- Serial 'N0. 754,415.

ication by distillation at this temperature, however,- is in practicevery ditiicult because of '.he fact that the necessary apparatusdeteriorates rapidly at such a high temperature. .By reducing thepressure in the apparatus, i. e. by carrying on the distillation underdiminished pressure, the boiling point of the metal can be reduced,until it coincides with the melting point at a pressure of approximately2 millimeters of mercury, thus reducing the difficulty found inproducing suitable apparatus of a suiiicient size to handle commercialquantities of metal. and strong enough to satisfactorily withstand theexternal pressure involved.

I have discovered-` however, -that if the pressure inside the apparatusis still further at the temperature of the sblid metal being sublimed isslightly greater than the total pressure within the condenser. Underthese conditions, the evolution of magnesium vapor Will be rapid and ifthe proper condensation facilities are provided the rate of sublimationis only limited by the rate at which heat can be supplied to the metalbeing sublimed. This point at which the vapor pressure of the solidmagnesium becomes grcater.than the absolute pressure of the system ishereinafter called the sublimation point.

ABy virtue of operating at or above the sublimation point, I not onlyproduce rapid sublimation, but by the rush of magnesium vapor toward thecondenser I sweep out and away the residual amountv of air orv other gasin the apparatus, and thus reduce very much the tendency of this as'tocombine with the magnesium and ren er the product impure.

One of the great advantages of my meth- 0d of sublimation as comparedwith vacuum distillation of magnesium is that not only can it be made tobe as rapid as the distillation but it also gives a considerably purerproduct. In vacuum distillation I have rapidly.

, taminates the distillate, but its formation appears to be prevented bysubliming rather than distilling the magnesium so as to avoid thephenomenon of the evolution ofbubblcs from a liquid.

It will he apprehended that the process is capablu of being carriedoutin a number of Vdifferent types of apparatus and that the one shown anddescribed is merely illustrative of the principles of the invention.This embodiment', however. has been found to be practical inconstruction and operation and eflicient in use.

Referring to the drawings for a more complete disclosire of theinventionzy Figure l is a vertical longitudinal .section of the furnace;

Figure 2 is a section on the line 2-2 of Figure l;

Figure 3 is a 'detail of the cover and closing mechanism for the retort;

Figure 4 is asection on the line 4-4 of Figure l; and

Figure 5 isa view showing a fragment of my new product.

The iron retort 1 issuitably supported and inclosed in a brickwork andmay be heated ,by burners projecting through the openings 2 and 3 in thelower corners of the combustion chamber, or in any other suitablemanner. The retort at its lower end is supported by the vertical brickwall 5 and by the wall collar 6. Intermediate the ends, it is supportedby a wall collar 7 carried by the center wall 8. At its front end it issupported by the wall collar 9carricd by the front wall 10. In such aconstruction, the greater part of the retort is in the zone of heat, theremainder extending out into the air to provide a cold end therefor,which full size .may be provided with cooling coils.

The charging end of the retort is closed by asuitable door 11 which isso constructed as to -rnake the same as gas tight as possible. Asuitable construction comprises lugs 13 integral with the retort andaseries of hooks 20 welded'to the lugs and clampedbetween the bars 14 ofthe framework 15. Carried vbetween the said bars are screw blocks 16which engage with the screws 17 of the hand wheels 18. Rotation of thesaid wheels in a suit-able direction will loosen or tighten they andlatl its lower end rests on the annular.

ring 23, integral with the pot, the other end extending up to theclosing flange. The purpose of the ring 23 is to keep the liner fromslipping down into the retort and also to form a seal so that gaseousmagnesiun'i does Lot travel up between the liner and the lretort wall.The liner may be made in one piece or split longitudinally into twohalves, tol facilitate removal of the deposited -crys ta s,

peratz'on.

' The pot is charged with a suitable quantity of crude, alloyed orimpure magnesium, sealed and vacuum applied. When the manometer showsthat the desired degree vof4 vacuum has been obtained, heat is applied,

care being taken to ,maintain the vacuum.

After a period of time, the temperature will rise to about 600o C. Under`the residual pressure employed the temperature will remain practicallyconstant at about 600O C.l

Further application of heat merely increases the rate of sublimation anddoes not appreciably change the temperature of the metal being sublimed.Thus it is impossible to melt the metal with any reasonable applicationof heat. When sublimation is complete as indicated by an abrupt rise internperature, the source of heat is cut off and the .etort allowed tocoolk while still under the Same vacuum.

f Under the conditions outlined,- the magnesium'doesnot melt but passesdirectly.

from the solid into the vapor state. The

vapor passes into the cooler portion of the'- retort where it condenseson the liner. When opened, the inner surface of the liner wlll be foundto`be covered withl crystallized magnesium in the form of a looselycohering mass of aggregated crystals which can 'oe removed in a suitablemanner. Analysis of the residue in the bottom-of the retort will showthat nearly all the magnesiumhas been vaporize'd: Analysis of thecrystals of mag. nesium will show that the magnesium content may be ashigh as 99.989%. y

The best availabledatalindicate that the vapor pressure ofmagnesiumdecreases `from one atmosphere or 760 mm. of mercury yat 1120C., which is ordinarily spoken of as itsboiling point, -to approximately2 mm. at its melting point, 651 C. Below the melting point the vapor'pressure-,de-

. creases so that after a further drop of about 270 C. it is about 0.001mm. If crude, impure, or alloyed magnesium is heated at a temperaturebelow its melting point, the magnesium will vaporize so as to produce apartial pressure of magnesium vapor, determined by the temperature. Ifthis heating is done in the presence of an inert gas such as argon, atatmosphere pressure or under diminishedV pressure, but still at a totalpressure greater than the vapor pressure of magnesium at the temperatureemployed, this magnesium vapor will diifuse through the inert gas; andif another part of the apparatus is cooler than the metal being heated,magnesium will gradually condense in this portion of the apparatus.y

This rate of sublimation is very slow, but I have found that if thetotal pressure within the condenser is reduced to a point below thevapor pressure of the magnesium at the temperature employed (as measuredat 19, Fig. l), rapid sublimation takes place. Instead of having toslowly .diffuse through the inert gas present, the magnesium vapor willthen be rapidly evolved at a sutlicient pressure to sweep this gas awayand into the condenser; where, by a suitable regulation of the condensertemperature, I continuously condense this vapor in the form of a verypure crystallized mass. In carrying out my process, soliditication ofthe' magnesium vapor without crystallization may occur if the condenseris too' cold. The temperature of the condenser, therefore, must be highenough to permit continued condensation and re-evaporation of themolecules such as is necessary in the produc' tion of crystals from anyvapor.

It is, of course, necessary that the temperature in the condensing4 areashould be below that of the metal being sublimed, since the differencein vapor pressure due to thisidifference in temperature is the drivingforce causing the rapid transfer of the magnesium vapor from thesubliming'to the condensing end of the system. This difference inpressurey must be equal to thesum of the partial pressure of the inertgas present in the condenser and the pressure required to overcome thefrictional resistance and force the vapor from the subliming to thecon-l densing end. This importance of these factors is seen by the factthat calculation shows that if magnesium be sublimed in an apparatussuch as the one shown in Fig. l, having a cross-sectional area of onesquare foot at the section LPA, at a temperature of 600o C. and apressure of 0.75 mm., the linear. velocity of the magnesium vapor whichwould be necessary to sublime 100 pounds of magnesium in 24 hours wouldbe in excess of one-half mile a minute. Diffusion, such as would takeplace if the total pressure within the apparatus were greater than thevapor pressure of magnesium at the temperature employed, is known totake place relatively slowly, and it is evident that my method ofsublimation of magnesium will be much more rapid than one which dependsupon diffusion.

The temperature of sublimation and conversely of solidification may varyfrom approximately 300 C. at .001 mm. pressure to 651 C. atapproximately 2 mm. pressure. The most favorable operating conditions atthe present time have been found to be a temperature of approximately(500o C. and a pressure of 0.5 to 0.2 mm. Under such conditions .I amable to sublime 100 pounds of magnesium i114 hours in an apparatushaving a cross-section of approxinn-.tely one square foot.

lVhen the liner is removed it is found that impurities, such as sodium,which are more volatile than magnesium and which therefore vaporize andgo into the con denser, are segregated at the upper or cooler end of theliner and may be readily removed.

The specimen shown in Figure 5 is a fragment of the crystallized masswhich adheres to the surface of the liner along the line 25. The surface26 may show fully developed crystal faces of magnesium. The crystalsvary in size and some may have crystal faces as large as one-"fourth ofa square inch in area or more. vBeing coherent, the masses can bereadily handled but since they are only loosely coherent, they can bereadily broken into pieces suitable for subsequent manufacturingoperations.

In using the term sublimed crystals of magnesium in the claims, I havereference to a product produced by a process wherein the. crystals arequite Vfree to grow in part,

and where during this growth the faces of` many of tne crystals assumetheir typical external shape. v

Magnesium which has solidified from the liquid state is crystalline butnot crystallized. It is composed of\ closely coherent grains having acrystalline structure and which while forming were not free to grow andassume their typical external shape.

Crystallized metal as produced by my process is exceedingly pure. Byvirtue of the absence of reactive agents such as nitrogen and oxygen,the crystallized mass is substantially free from admixed oxides ornitrides.

The crystallized metal can be subjected to various further operations.vIt can be 'satisfactorily melted or it can be placed without melting inan extrusion press and extruded directly into any of the customarystructural shapes suchas wire,bars,4 rods, etc., having physicalproperties equivalent to those of similar shapes extruded from castbillets.

pressed directly into briquets at a temperature of about 200o C. or evenlower if sulficient pressure is available. Both the direct extrusion anddirect-compression give a substantially pure metal in marketable form.Such metal is substantially free from admixed magnesium oxide andrmagnesium nitride which might not be the case ifthe metal were meltedbefore being extruded or compressed. Y

On account of its extreme purity, crystallized magnesium as made by myprocess is more highly-resistant to corrosion by mois ture or theatmosphere than any other commercial magnesium of which I have anyknowledge. This resistance to corrosion is maintained through anysubsequent manipulation or process which does not allow the formation orintroduction of impurities.

I claim:

1. As a new commercial product, a mass of subli'med crystals ofmagnesium.

2. As a new commercial product, coherent aggregates of sublimed crystalsof magnesium.

3. As a new commercial product, loosely coherent aggregates of sublimedcrystals of magnesium 4. As a new commercial product, a mass of sublimedcrystals of magnesium,substan 'tially free from nonmetallic impurities.

5. As a newrommercial product, a mass of sublimed crystals of magnesiumcontaining` less than 0.1% of other metals.

6. As a new commercial product, a mass of sublimed crystals of magnesiumcontaining less than l0.02% of other metals.

In testimony whereof I affix my signature.

HERMAN E. BAKKEN'.

